ASoC: sun8i-codec: Add a comment on the LRCK inversion

The current code might be a bit intriguing without having experienced the
issue before, and might come up as a mistake.

Make explicit what's going on by adding a comment.

Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

1 files changed, 11 insertions, 0 deletions

diff --git a/sound/soc/sunxi/sun8i-codec.c b/sound/soc/sunxi/sun8i-codec.c
index c2ceca485d6a..b3329692e3dc 100644
--- a/sound/soc/sunxi/sun8i-codec.c
+++ b/sound/soc/sunxi/sun8i-codec.c
@@ -197,6 +197,17 @@ static int sun8i_set_fmt(struct snd_soc_dai *dai, unsigned int fmt)
         regmap_update_bits(scodec->regmap, SUN8I_AIF1CLK_CTRL,
                            BIT(SUN8I_AIF1CLK_CTRL_AIF1_BCLK_INV),
                            value << SUN8I_AIF1CLK_CTRL_AIF1_BCLK_INV);
+
+        /*
+         * It appears that the DAI and the codec don't share the same
+         * polarity for the LRCK signal when they mean 'normal' and
+         * 'inverted' in the datasheet.
+         *
+         * Since the DAI here is our regular i2s driver that have been
+         * tested with way more codecs than just this one, it means
+         * that the codec probably gets it backward, and we have to
+         * invert the value here.
+         */
         regmap_update_bits(scodec->regmap, SUN8I_AIF1CLK_CTRL,
                            BIT(SUN8I_AIF1CLK_CTRL_AIF1_LRCK_INV),
                            !value << SUN8I_AIF1CLK_CTRL_AIF1_LRCK_INV);